The present invention relates to coverings over containers that house volatile chemicals. More particularly it relates to multi-layer membranes which can divide into a gas permeable laminate that is permanently affixed to the container, and a peel-off gas impermeable layer.
A variety of volatiles are contained in containers that have a membrane closure. The closure is in the form of a multi-layer film structure configured such that a lower membrane section of the structure is permeable to the volatile when the volatile is in a gas phase, and is permanently affixed to an otherwise open end of the container. There is also an upper membrane section of the closure that is a peel-off type lid that is impermeable to the gas volatile. Before the lid is peeled off, the volatile is trapped in the container. When the lid is peeled off the volatile (to the extent in a gas phase) can begin to escape for its intended purpose. See e.g. U.S. Pat. Nos. 4,055,672, 4,849,606, 5,518,790 and 6,722,578, and U.S. patent application publication 2007/0183932.
The volatile is often an air treatment chemical such as insect control agents (insecticides, insect repellents, insect growth regulators, insect attractants, synergists, etc.), fragrances and deodorizers. However, it may also be a use-up indicator chemical whose volatilization rate has been coordinated with the use-up rate of an air treatment chemical that is also being volatized. Often the volatilization occurs when the container is heated by an external source of heat. However, the volatization may optionally occur even though no additional heat is applied.
Regardless, such systems are typically designed so that volatilization shouldn't begin prior to the consumer placing the product in use. Hence, it is important that a peel-off structure used to initiate these products have a sufficient seal to the permeable membrane so as to effectively prevent premature leakage of the volatile during storage prior to use. This is made somewhat more complicated by the need for the bond between the upper and lower sections of the structure to be sufficiently weak so that the upper section can readily be pulled off it without disturbing the bond between the lower section and the container.
Further complicating matters is that such structures are sometimes exposed to temperatures over 50° C. (e.g. in a transport truck in the desert during the summer). This can degrade certain bonds. Moreover, it has been learned that some preferred volatiles, especially under elevated temperature conditions, can act to further degrade the bond between the peel-off portion and the permanent permeable portion.
Thus, a need exists for improved multi-layer film coverings for volatizing dispensers, particularly where the coverings have a reduced risk of leakage prior to use.